Apache Flex, formerly Adobe Flex, is a software development kit (SDK) for the development and deployment of cross-platform rich Internet applications based on the Adobe Flash platform. Initially developed by Macromedia and then acquired by Adobe Systems, Adobe donated Flex to the Apache Software Foundation in 2011 and promoted to a top-level project in December 2012.The Flex 3 SDK was released under the open source Mozilla Public License in 2008.